A particular growth area within the wider field of wireless access services is that of location-based services. A service provider can use a knowledge of a terminal's location to enhance user experience, to create new and potentially valuable revenue streams for the service providers, and to implement novel subscriber tariffs. The Mobile Location Protocol (MLP) is a protocol specified by the Open Mobile Alliance (OMA) to provide (network-based) applications with location information independently of the underlying network technology [LIF TS 101]. It relies upon the delivery of XML documents containing location information from a mobile location centre within the wireless network to a service provider's server, typically using HTTP as the transport mechanism. 3GPP specifications for wireless network architectures (including GSM, 3G, and LTE) provide for the determination of location information suitable for use with MLP. This 3GPP “system” is referred to here as a Mobile Positioning System (MPS). The MPS is facilitated by a Gateway Mobile Location Centre (GMLC) defined in GSM and UMTS, or possibly by a Mobile Positioning Centre (MPC) which is defined in the American National Standards Institute (ANSI) standards. FIG. 1 illustrates the MLP message exchange involving the Standard Location Immediate Request (SLIR) and Standard Location Immediate Answer (SLIA).
The GMLC (or MPC) returns to the location-based application (of the service provider), a “location area” representing the area where the terminal (or loosely speaking the subscriber) is located. This location area could, for example, be a circle represented by a centre origin and a radius where the origin corresponds to the (inaccurately determined) subscriber location and the radius represents a degree of uncertainty. Services such as so-called ‘Home Zone’ applications—which compare the actual (assumed) location with pre-set coordinates to apply differentiated charging, mobility restrictions etc.—rely on MPS to request the location of a subscriber.
Many variables determine the accuracy of mobile positioning, including:                The current volume of traffic handled by a radio mast;        Radio interference;        Reflections off tall buildings;        Current weather conditions; and        Radio planning (e.g. mast density in urban versus rural areas)        
As such, the location areas provided by MPS for subscribers can be inaccurate. Another variable that is often overlooked is the accuracy of the coordinates stored by the location-based application (e.g. Home Zone) that are to be compared against the MPS location areas. These coordinates may be provided by the 3GPP network operator, or by a third party (e.g. based upon GPS coordinates) and guarantees as to their accuracy cannot always be given. In some cases, the stored coordinates are themselves generated by the MPS and are therefore subject to the inaccuracies of MPS. This could happen when coordinates are recorded when a subscriber designates a Home Zone using some terminal-based selection process, whereupon the MPS logs the subscriber's current position and passes this to the service provider.